There are many forms of mass storage technology used in modern computing. One of the prevailing forms of data recording is magnetic data recording due to its large storage capacity and re-usable recording media. Magnetic data recording may be implemented by employing different types of magnetic recording media, including tapes, hard discs, floppy discs, etc. Over the years, significant developments have been made to increase the areal data recording density in magnetic data recording to raise its capacity.
One approach for increasing the areal density of high capacity magnetic recording devices is to decrease the size of individual magnetic particles (grains) in the magnetic recording layer. In general, smaller magnetic grains are required to reduce the intrinsic media noise and to obtain a higher signal-to-noise ratio during the data reading process. However, if the magnetic grain size is too small (diameter less than approximately 8-10 nm), thermal excitation will perturb the magnetization of the magnetic grain and cause instability in the magnetization. This is known as superparamagnetic instability and may render today's commonly used cobalt-alloy based recording media unsuitable for archival data storage purposes. In perpendicular recording media, the grain magnetization is oriented perpendicular to the disk surface. By utilizing a soft magnetic underlayer and a single pole write head more efficient magnetic flux flow is achieved, thus enabling smaller grains to be kept thermally stable than is possible in longitudinal recording.
One approach toward reducing the grain volume V while avoiding superparamagnetic instability is to use a magnetic material with a high magnetic crystalline anisotropy energy density Ku. A promising material with high Ku and good chemical stability is iron-platinum (FePt), and in particular L10 crystalline FePt nanoparticles. It has been proposed that L10 crystalline FePt nanoparticles (dia<5 nm) may be used to create an ultra-thin magnetic recording layer with very small grain volumes. Therefore, FePt nanoparticles have the potential to act as the recording media for high-density data recording of 1 Terabit/in and beyond.
It has been disclosed that an ultra-thin layer of FePt nanoparticles can be deposited onto a substrate by dip-coating the substrate in a solution made up of FePt nanoparticles, a non-polar solvent and excess surfactant. Creating a uniform (equal spatial distribution) and well-ordered (constant lattice structure) layer of FePt nanoparticles through dip-coating remains difficult. High data density recording media require the FePt nanoparticles to self-assemble into uniform ordered arrays across the substrate surface on length scales of several centimeters. Current nanoparticle deposition methods on solid surfaces show self-assembly in an organized monolayer only on length scales of several micrometers. Large-scale uniformity has currently been achieved in bilayer and multilayer deposition, but without the necessary long-range ordering.
Further details of FePt nanoparticles deposition through dip-coating may be referred from the technical paper by N. Shukla, J. Ahner, and D. Weller, “Dip-coating of FePt Nanoparticles Films: Surfactant Effects”, Journal of Magnetism and Magnetic Materials, Vol. 272-276 (2004) 1349, which is incorporated by reference as if fully set forth herein.
Another challenge with using FePt nanoparticles is that they require a subsequent annealing at a temperature range of 500° C. to 750° C. in order to convert their crystalline structure from a non-magnetic face-centered cubic structure to a magnetic face-centered tetragonal structure. When FePt nanoparticles are exposed to this high temperature, the thermal energy will permit the nanoparticles to clump together (coalesce) and form much larger particles resulting in a loss of uniformity. This uniformity loss due to thermal energy is known as sintering damage and it appears more frequently when the nanoparticles are deposited as a bilayer or a multilayer. One approach that may reduce such damage from sintering is to deposit the FePt nanoparticles as an organized monolayer. However, when a FePt nanoparticle monolayer is exposed to the high temperature of the annealing process, it may experience a loss of self-assembly which will result in poor magnetic properties.
Accordingly, it would be desirable to develop a high capacity recording layer for a mass storage apparatus, which can take full advantage of FePt nanoparticles in a structure that can withstand the annealing process without experiencing sintering or loss of self-assembly problems.